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tricky shell script question


From: Erik-Jan Taal
Subject: tricky shell script question
Date: Tue, 12 Feb 2008 17:17:14 +0000

Hello,

Anyone know the answer to this?

Suppose the following scenario:

Edit new file 'p.sh' in vim.

Add these lines :

#!/bin/sh
sleep 30

Now save the file in vim with ':w' and chmod +x it. Then open another terminal 
and run the script. While that's sleeping, quickly add the following line to 
the end of the script:

echo bla

Now watch the terminal where the script was still running. I would
expect no output to be given, as I assumed the script is read into memory
at startup and not during execution and this is what happens on most 
systems. On one server however, the 'bla' is echoed.

On another system, which has as far as I can tell the same OS configuration, 
same version of bash (RHEL ES release 3; bash-2.05b-29.0.3),
same options displayed in 'shopt', same output if doing 'lsof | grep p.sh',
the script is runs as I initially expected, not outputting the 'bla' and I 
haven't seen the above mentioned behaviour before in 7 years of working 
with shell scripts.

What is the toggle or switch that makes it output this 'bla' on that particular 
server or in other words, why is the script being kept open and apparently 
read line by line? (10 nerd points for those with the right answer ;)

Please cc me at this email address as I'm not subscribed to the list.

thanks and kind regards,
Erik

-- 
Erik Taal
ICT Systems Administration, West Midlands Fire Service
Streetsbrook Road, Solihull, West Midlands, B91 1QY
tel: 0121 380 6572          | fax: 0121 711 1699
mob: 077 6988 1400 (wmfs)   | mob: 079 3187 5526 (backup)
pag: 076 5975 0398
 
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